Although serial killers make frequent appearances in TV shows and movies, and are often reported on disproportionately by the news, most of us know that they’re not really much of a threat in the big scheme of things. Statistically speaking, you aren’t very likely to be murdered in most places, and only a small percentage of murders are committed by serial killers. The image crafted by the media of the cold, brilliant, and ruthless killer who stalks people for nothing more than sport and pleasure, is an outlier in the real world.

However, though their ranks are incredibly small, there may be more of them lurking in our cities and highways than we realize. That’s the conclusion that former journalist Thomas Hargrove came to, after he developed a computer algorithm which can spot serial killers who are often overlooked by the police. He told Bloomberg that “I think there are a great many uncaught serial killers out there…I think most cities have at least a few.”

The algorithm works by sifting through homicide data provided by the FBI and local police departments, and searches for patterns in geography, cause of death, age group and gender. Since most serial killers frequently kill the same kinds of people in the same ways over and over, the algorithm works quite well. In fact, Hargrove’s algorithm spotted a serial killer in Gary, Indiana. He warned the police in Gary that a killer was in their midst several times in 2010, but his emails were ignored. The culprit was found 4 years later after he had killed seven more women.

Hargrove’s program has also spotted serial killers in Los Angeles and Phoenix who wouldn’t be caught for several years. But he warns that there are plenty more who haven’t been caught. “The whole point of the algorithm was to find the low-hanging fruit, the obvious clusters. But there were dozens and dozens of them all over the country.”